Abstract 4150: An HPK1 inhibitor CMPD0431 is a novel immuno-oncology agent that induces anti-tumor effects

Hematopoietic progenitor kinase 1 (HPK1, MAP4K1) is a serine/threonine kinase and a member of MAP4K. HPK1 is prominently expressed in subsets of hematopoietic cell lineages. HPK1 is a newly identified as a critical negative regulator in the activation of T lymphocytes and dendritic cells. It has been recently demonstrated that the important roles for kinase activity of HPK1 in anti-cancer immunity as a new intracellular checkpoint molecule as well as potential advantages of combination therapy with current checkpoint regimens. HPK1 inhibition is expected to have dual functions, 1. prolonged activation of T cells; 2. enhanced APC functions by dendritic cells. This dual targeting may synergistically work together for efficient immune responses in tumor microenvironment. We have developed a series of small molecule inhibitors of HPK1 with a lead compound of CMPD0431, which are orally available with good physicochemical and pharmacokinetic profiles. CMPD0431 and its series demonstrated good potency for HPK1 with kinase IC50 values of ~20 nM or under. Treatment of T cells with CMPD0431 successfully blocked serine 376 phosphorylation of SLP76, a critical biomarker substrate for HPK1 and also for downstream signaling in T cell activation, leading to sustained activation in human T cells. CMPD0431 was shown to increase the CD3/CD28-induced proliferation of human primary T cells with enhanced production of pro-inflammatory cytokines such as IFN-γ and IL-2. Furthermore, CMPD0431 enhanced the functional activity of antigen presentation with increased level of pro-inflammatory cytokine productions in mouse bone marrow-derived dendritic cells. All together, we have confirmed that HPK1 inhibition indeed play a dual function in T cells and dendritic cells to effectively promote cancer immunity. In the CT-26 syngeneic mouse model, we showed that CMPD0431 inhibited tumor growth with increased intratumoral infiltration of CD3+ lymphocytes and with increased pro-inflammatory cytokine production, demonstrating promoted cancer immunity with a potential for conversion of cold tumor into hot tumor. A subset of mice with high dose treatment of CMPD0431 showed a tumor regression with no further tumor regrowth for 20 days without compound treatment. The cured mouse group did not grow tumor even after re-challenging with CT-26 without compound treatment, demonstrating the effective immunological memory by CMPD0431. Those immune memory mouse group displayed increased secretion of IFN-γ by splenic T lymphocytes with enhanced response to the stimulation by CT-26 specific antigen, AH1 peptide. All together, these results support further development of CMPD0431 and its derivatives, first-in-class and advanced leads of HPK1 inhibitors with novel mechanism of action to be applied as a single-agent or combinational therapy with the current checkpoint inhibitors. Citation Format: Seungmook Lim, A Yeong Park, Misoon Kim, Gyooseung Jung, Suyeon Jo, Keonseung Lim, Gwibin Lee, Heekyoung Yang, Hyonam Kim, Hyeongjun Kim, Minwoo Lee, Jamie Jae Eun Kim, Jinhwa Lee. An HPK1 inhibitor CMPD0431 is a novel immuno-oncology agent that induces anti-tumor effects [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4150.